Cellular Respiration

Topics: Adenosine triphosphate, Cellular respiration, Glycolysis Pages: 5 (1236 words) Published: December 10, 2013
Cellular Respiration

OVERALL EQUATION:
C6H12O6(aq) + 6O2(g) -> 6CO2(g) + 6H2O(l)
3 OVERALL GOALS:
1. Break bonds between the 6-carbon molecules of glucose – results in 6 CO2 molecules 2. Move hydrogen atom electrons from glucose to O2, forms 6 H2O molecules 3. Trap as much free energy released as possible in the form of ATP

Stage 1: Glycolysis
Cytoplasm, 10 reactions, anaerobic
Stage 2: Pyruvate Oxidation
Mitochondrial matrix, 1 step process
Stage 3: The Krebs Cycle
Mitochondrial matrix, 8 steps in a cycle
Stage 4: Electron Transport Chain & Chemiosmosis (Oxidative Phosphorylation) Mitochondrial membrane, various steps

ATP Formation
Substrate Level Phosphorylation:
ATP formed directly
Enzyme-catalyzed reaction
A compound that has phosphate in it, transfers a phosphate group directly to ADP Forms ATP, fig on pg. 95
Oxidative Phosphorylation:
ATP formed indirectly
Oxidative because it involves redox reactions, with O2 being the last electron acceptor More complicated than Substrate-Level, but yield more ATP for each glucose molecule processed NAD+ removes 2 H atoms (2 p+, 2 e-) from original glucose molecule NAD+ becomes reduced, forming NADH, after attaching 1 p+ and 2 e- The remaining p+ dissolves into the surrounding solution as H+(aq) This occurs in one reaction in Glycolysis, during Pyruvate Oxidation & during 3 reactions in the Krebs Cycle Another coenzyme called FAD performs a similar function

FAD is also reduced by 2 H atoms and is reduced to FADH2 because all of the p+ & e- bind to it This occurs in one reaction in the Krebs Cycle
The reduction of NAD+ & FAD are energy-harvesting reactions that will eventually transfer free energy to ATP molecules

Glycolysis
Carbon backbone of glucose splits in half, forming two 3-carbon pyruvate molecules Each step is catalyzed by a specific enzyme
Step One:
ATP phosphorylates glucose to glucose 6-phosphate
Phosphate group is added to glucose by the enzyme Hexokinase One ATP molecule is used to do this & becomes ADP
Step Two:
Glucose 6-phosphate is rearranged to fructose 6-phosphate
Occurs by the enzyme Isomerase
Step Three:
ATP phosphorylates fructose 6-phosphate into Fructose 1 & 6-bisphosphate (unstable) One ATP molecule is used to do this & becomes ATP
Occurs by the enzyme Phosphofructokinase
Step Four-Five:
Since Fructose 1 and 6-bisphosphate are unstable, they split into Dihydroxyacetone phosphate (DHAP) and Glyceraldehyde 3-phosphate (G3P) DHAP is converted into G3P which results in two G3P molecules being formed This occurs by the isomerase enzyme

Step Six:
Two NADH molecules are produced, one each from the two G3P molecules that were produced in Step 4-5 The two G3P molecules become two 1,3-disphosphoglycerate molecules (BPG) Step Seven:
The two DPG molecules become 3-phosphoglycerate (3PG)
The phosphate group on the BPG phosphorylates the ADP and makes it into ATP So two ATP’s are produced, one from each of the two DPG molecules Step Eight:
3PG is rearranged to 2PG since the phosphate group was used to make ATP in step 7 Step Nine:
The enzyme Enolase removes a water molecule and the 2PG molecules are converted into PEP (phosphoenolpyruvate)

Step Ten:
PEP is converted to pyruvate by the enzyme Pyruvate Kinase
Phosphate group on PEP phosphorylates ADP into ATP
Two more ATP molecules are produced

The overall chemical equation for glycolysis is:
glucose + 2ADP + 2Pi + 2NAD+ -> 2 pyruvate + 2ATP + 2(NADH + H+) Overall during glycolysis, 2 ATP are produced (two were used in the beginning, results in only two in the end) and 2 NADH are produced The 2 ATP produced may be used by the cell immediately and the 2 NADH may be processed further by cells to obtain more ATP

Pyruvate Oxidation
The two pyruvate molecules that are formed in glycolysis are transported into the mitochondrial matrix Three changes happen here:
Carboxyl group is removed as CO2
NAD+ is reduced by 2 H atoms, obtained from food. The remaining two...
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